Modern wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines of this kind generally comprise a tower and a rotor arranged on the tower. The rotor, which typically comprises a hub and a plurality of blades, is set into rotation under the influence of the wind on the blades. Said rotation is normally transmitted through a rotor shaft to a generator, either directly or through the use of a gearbox. This way, the generator can produce electricity which can be supplied to the electrical grid.
Particularly for offshore wind turbines, direct drive systems employing permanent magnets are usually chosen. A permanent magnet generator may be defined as a generator where the excitation field is provided by permanent magnets instead of coils (electromagnets).
Permanent magnets may be attached to the rotor in different ways, such as e.g. glued to a rotor body, by stamping the ends of the magnets to hold them in place, through the use of clamps coupled to the rotor body or directly to the rotor rim, by welding, through bolted connections, etc.
Assembling a large generator may require complicated, costly and lengthy processes.
For example, large amounts of welding, bolts, glue, etc. and their processing may be required for fastening magnets to a generator rotor and coils to a stator. Processes of welding, gluing, screwing etc. may be time consuming and labour intensive. Hence, prior art approaches of fastening items in an electrical machine may be rather complex and expensive.
Besides, when glue is used, fastening of one item to another may deteriorate over time. Therefore, in this case, the attachment may not be reliable enough after a certain time of its implementation.
In order to improve the assembly process, it is known to provide permanent magnet modules, which may be attached to the rotor as a single item.
A permanent magnet module may be defined as a unit having a plurality of permanent magnets, such that the plurality of magnets can be mounted and unmounted together. Such a module may have a module base with a shape suitable for housing a plurality of permanent magnets that may be fixed to the base. The base may be configured to be fixed to a rotor rim in such a way that the plurality of magnets are fixed together to the rotor rim through the module base. The use of permanent magnet modules may facilitate the manufacturing of a generator rotor.
In an electrical machine (e.g. a wind turbine generator), coils are necessary with the role of e.g. generating an electric current as a result of their interaction with the magnetic (or excitation) field generated by e.g. permanent magnets. The coils may also be arranged in modules including a plurality of stator teeth. A stator tooth, which may support one or more coils, is typically fastened to a corresponding housing of the stator.
For the sake of simplicity, a group or assembly of stator teeth with attached coils may also be referred to herein as a coil module. Stator teeth may be attached to the stator based on the same foundations or similar to those commented with respect to attaching permanent magnets to the rotor, based on e.g. welding, bolted connections, etc.
Coil modules may be defined in a similar way as permanent magnet modules have been defined before. In this case, however, coil modules support coils instead of permanent magnets, and coil modules are typically attached to the stator instead of to the rotor.
Coil modules and permanent magnet modules may have a module base formed as a stack of sheets which may be separated from each other by means of electrically insulating material. With this feature, eddy currents may be reduced in corresponding electrical machine such that its efficiency may be improved.
Generators of considerable dimensions and having the same necessity (of fastening one item to another item) may also be found in e.g. steam turbines and water turbines.
The present disclosure aims at improving the prior art systems for fastening an item to another item in an electrical machine.